The present invention is generally related to steam generators with lance type water cannons for cleaning heat transfer surfaces. More particularly, the present invention is directed to a method and system for controlling the positioning of the water cannon lance by measuring the angular displacements of the lance with respect to the wall on which the water cannon is mounted.
Large steam generators such as boilers have a combustion chamber and heat transfer surfaces on which soot and ash deposits build up as a result of the combustion process. The soot and ash buildup form a contamination layer on the heat transfer surfaces that reduces the heat exchange efficiency of the boiler. Some of the negative impacts of the thermal efficiency of these boilers are: (1) added fuel consumption in order to maintain the proper steam conditions that are required by the downstream processes; and (2) an increase in boiler flue gas temperature leading to increased fouling and plugging of the gas passages requiring the boiler to be taken off line to be cleaned.
In order to combat the buildup of ash, boilers are fitted with automatic cleaning devices known as soot blowers. There are many types of soot blowers based on boiler design as well as the area of the boiler that needs to be cleaned. In the case of boilers burning fossil fuels such as coal or heavy oil, there also is a need to clean the walls of the boiler in the area known as the lower furnace or hearth.
In this area of the boiler, the walls are comprised of tubes that are positioned side by side to form a box type shape. Fuel such as coal or oil is introduced into the cavity of this box (hearth) where it is burned. High pressure water flows through the inside of the tubes and is used to absorb the heat. In doing so, the water eventually picks up enough heat to be converted into steam.
Some of the residue of combustion adheres to the walls of the hearth inhibiting the transfer of heat. There are three methods in the prior art that have been used for cleaning the furnace wall: (1) traditional soot (wall) blowers containing a lance tube, and introduced through an opening in the boiler wall, eject steam/air back towards the wall; (2) water blowers that eject water back towards the wall; and (3) water cannons that eject water toward opposing or adjacent side walls.
Lance-type water cannons inserted through a front wall of the generator are used to direct a stream of fluid to clean the heat transfer surfaces. However, not all heat transfer surfaces develop an ash buildup at the same rate. Ash can accumulate more in one corner than in another. Likewise, more contamination by ash and soot can occur in one zone of a generator wall than in another zone of the same wall because of temperature differentials during the combustion process. The temperatures in some zones are higher than in others. The zones in which contaminants such as ash and soot build up more quickly require more frequent cleaning in order to retain heat exchange efficiency of the steam generator. Often sensors are installed in the furnace walls that measure the temperature or heat flux in order to determine the cleanliness of the heating surface that the water cannon is intended to keep in a clean condition. The information provided by the sensors is used in a control system to determine whether and where the water cannon shall clean.